Overview
Computational Fluid Dynamics (CFD) is becoming an increasingly important tool for analysing flows around ships and propulsors. CFD methods allow a better understanding of the flow phenomena around the hull, give physical insight in the flow characteristics and so can provide the background for design integration. Today's methods do, however, lack a final accuracy to match results obtained in experiments. The combination of improved accuracy applied in integrated design optimisation is the key to future ship design.
Facing an increased demand for seagoing freight and passenger transportation, the European shipbuilding and shipping industry will rely heavily on improved ships and ship design analysis tools.
This VIRTUE project addresses particular aspects such as the improvement of performance, efficiency, safety and environmental friendliness, which are, to a large extent, influenced by the hydrodynamic behaviour of a vessel.
The objective of the project is to develop a new high precision CFD tool, and further improve existing ones, in order to provide integrated and complete numerical analysis of marine hydrodynamic behaviour in a virtual environment: the virtual tank utility.
By improving the accuracy, flexibility and reliability of CFD predictions, and by integrating presently disparate tools into an integrated platform, VIRTUE promises to deliver important advantages to the shipbuilding industry, including:
- reduced manufacturing costs through shorter lead-times and more focused designs;
- improved design and product quality;
- increased range and quality of service offered by European hydrodynamics service providers and an increased market share in the design and analysis of maritime products; and
- increased R&D capacity of the sector as a whole.
VIRTUE's scientific and technological objectives to achieve these ambitious goals include:
- formally integrating numerical tools, using proven approaches, into an environment for complete modelling and simulation of ship behaviour at sea;
- providing smooth and versatile communication and data exchange links between marine CFD service providers, such as model basins, and the end user;
- providing the means (CFD tools, integration platform and optimisation techniques) to cover the whole range of hydrodynamic problems and to facilitate and support multi-disciplinary design optimisation of new ships.
Through large-scale international collaboration, bringing together the leading model basins in Europe, academia, software providers and marine consultants, VIRTUE improves and integrates state-of-the-art, high-precision CFD tools from a number of origins in a virtual environment, simulating ship behaviour at sea and providing an important complement to real test basins in the provision of marine hydrodynamic services.
The project integrates services and CFD tools from four different virtual tanks:
- the virtual towing tank;
- the virtual sea-keeping tank;
- the virtual manoeuvring tank;
- the virtual cavitation tank/tunnel.
The overall aim of the Virtual Towing Tank is to improve the accuracy, reliability and applicability of existing state-of-the-art CFD codes, through improving problem set-up and methodology, in order to develop a viable alternative to the physical towing tank testing in the prediction of hydrodynamic performance of ships, in particular the speed-power relationship, at the design stage. Also the aim is the application of the methods in dedicated optimisation process.
The overall aim of the Virtual Sea-keeping Tank is to address specific problems that cannot be dealt with model basins such as roll damping predictions, large amplitude and non linear motions, slamming / whipping, flooding, sloshing.
The overall aim of the Virtual Manoeuvring Tank is to use and further develop advanced CFD tools for predicting the manoeuvring performance of ships. The main approach developed here is based on using series of numerical flow simulations for prescribed simple (uniform or harmonic) modes of motion mirroring captive model tests.
The overall aim of the Virtual Cavitation Tank is to develop and validate a limited number of promising codes that are able to predict the flow about both non-cavitating (necessary for cavitation inception) and cavitating propulsors, and are in particular able to compute the adverse effect it has on the propulsion characteristics (such as radiated pressure fluctuations and cavitation erosion).
Finally a group of activities are finalised to the development of an integration platform, which provides the prerequisites for an integrated optimisation based on common standards for data provision and the presentation of results.
Funding
Results
The members of the VIRTUE consortium have been striving for scientific innovation and excellence in the most relevant technological areas of numerical hydrodynamics with the long term vision of being able to thoroughly complement experimental ship hydrodynamics using numerical methods. At the end of the VIRTUE project it is evident that the state-of-the-art of numerical hydrodynamics has advanced considerably and the overall objective to make CFD methods fit for use in either routine work or application to frontier problems in maritime hydrodynamics has been largely achieved.
Based on the developments in all CFD related work packages in VIRTUE, a large variety of CFD tools can be reliably applied to a large range of hydrodynamic analysis tasks arranging from practical problems and considerations in the maritime industry. This is especially important in view of the ever increasing need for improved fuel savings and accompanying reductions of ship emissions which form a major issue in public discussion today.
New and improved CFD tools together with a comprehensive Best Practice Guideline document - which has been produced from contributions from all work packages covering areas such as resistance, propulsion, seakeeping, manoeuvring and propeller / cavitation predictions - provide a significant boost to numerical analysis of maritime flow problems.
Together with the software and process integration platform developed in work package 5, VIRTUE tools today offer an unprecedented opportunity to analyse and optimise new ship designs from a hydrodynamic perspective and hence contribute substantially to solving the pressing problems of the maritime industry.
Technical Implications
The availability of robust commercial Computational Fluid Dynamics (CFD) software and the rapid growth in processing power have led to an increasing use of CFD for the solutions of fluid engineering problems across all industrial sectors. The marine industry is no exception: computational methods are now routinely used, for example, to examine vessel boundary layer and wake, to predict propeller performance and to evaluate structural loads. There has been a growing awareness that computational methods can prove difficult to apply reliably i.e. with a known level of accuracy. This is in part due to CFD being a knowledge-based activity and, despite the availability of the computational software; the knowledge base embodied in the expert user is not available. In the past this has led to a number of initiatives that have sought to structure existing knowledge in the form of best practice advice.
Building on these the VIRTUE Best Practice Guidelines expand the scope to the novel state-of-the-art arrived at in the VIRTUE project. For the four main maritime applications, namely: Towing Tank, Sea keeping Tank, Manoeuvring Tank, Cavitation Tank application cases are discussed which have been chosen to reflect different stages of maturity for applying Computational Fluid Dynamics: Underlying Flow regime and Application challenge.
The Best Practise Guidelines support the CFD specialist and/or the naval architect by providing him specific guidelines for each application cases, by providing validation against experiments when available, by comparing with Potential Flow methods and by underlining the challenges faced by the current state of the art modelling.